On December 6, 1989, an armed man named Marc Lépine entered the École Polytechnique de Montreal, a university associated with the Université de Montreal in Montreal, Quebec, Canada. Polytechnique Montreal focuses on research and teaching in engineering and other applied and design disciplines. Lépine entered a classroom where a mechanical engineering class was taking place; he ordered the male students (who were most of the students in the classroom) to leave, threatening them at gunpoint. When the male students had left, Lépine opened fire on the nine female students remaining; while doing so, he made statements about his hatred for feminists. Six of these nine students died. Lépine then roamed through the school, shooting at any female students he could find. In the end, he killed a total of 14 women before shooting himself inside the school.

In her novel, Penny describes these events from the perspective of a fictional character (Armand Gamache), but includes many historically accurate details. Nathalie Provost, who appears in the novel, is a historical figure who was shot and wounded by Lépine and has spent much of her life advocating for better gun control in Canada. Penny also includes the accurate and chilling detail of a police official entering the site of the shooting to find the body of his own daughter.